docs: def _get_cost_function(self):
          """Compute the cost of the Mittens objective function.
  
          If self.mittens = 0, this is the same as the cost of GloVe.
          """
          self.weights = tf.placeholder(
              tf.float32, shape=[self.n_words, self.n_words])
          self.log_coincidence = tf.placeholder(
              tf.float32, shape=[self.n_words, self.n_words])
          self.diffs = tf.subtract(self.model, self.log_coincidence)
          cost = tf.reduce_sum(
              0.5 * tf.multiply(self.weights, tf.square(self.diffs)))
          if self.mittens > 0:
              self.mittens = tf.constant(self.mittens, tf.float32)
              cost += self.mittens * tf.reduce_sum(
                  tf.multiply(
                      self.has_embedding,
                      self._tf_squared_euclidean(
                          tf.add(self.W, self.C),
                          self.original_embedding)))
          tf.summary.scalar("cost", cost)
          return cost